A known device for the roll-sealing of sheets is described in, for example, DE 100 52 218 A1. These devices consist essentially of a sealing roll and a mating roll, through which a shaped, molded sheet is transported along with a cover sheet. A heater raises the temperature of the sealing roll, which is pressed against the mating roll with a certain sealing force. As a result, the cover sheet is pressed against the molded sheet and bonded to it. The medication package is thus sealed. The combination of the parameters in question, namely, temperature, applied pressure of the sealing roll, and transport speed of the mating roll, generally determines the quality of the seal.
The molded sheet and the cover sheet are bonded together in the area where the sealing roll presses against the mating roll. The molded sheet comprises blister pockets, however, which must fit into corresponding recesses in the mating roll, so that a flat sealing surface is obtained. The contact area between the molded sheet and the sealing sheet is therefore not always of the same size; that is, the contact line is interrupted in the area where the recesses or blister pockets are located.
In cases where the sealing roll is pressed with a constant sealing force, the continuously changing contact area causes the pressure which is applied between the molded sheet and the cover sheet to vary. The result of this is that the sealing roll sinks into the composite sheet structure to various depths. This means in turn that the sheets are sealed in a nonuniform manner, and this lack of uniformity is visible on the medication package.
In the prior art, as in, for example, DE 10 2004 062 520 A1, various approaches have been taken to equalize the applied pressure by automatically controlling the sealing force of the sealing roll as a function of the positions of the recesses and blister pockets and thus to produce a more uniform sealing effect. This automatic sealing control, however, is highly complicated and is very difficult to manage at high machine speeds.
DE 10 2006 020 453 B3 describes a method for the production of sealing tools under consideration of a characteristic value for sealing quality, wherein the tolerances of the sealing tools and sheets are compensated by defining the penetration depth of opposing sets of ripples on the sealing roll and mating roll. This document provides a formula for the required ripple surface area A, wherein the rippled structure is distributed uniformly and symmetrically over the sealing roll and the mating roll. The use of rippled sealing rolls of this type also leads to nonuniform sealing effects, however, especially when a constant sealing force is used, because the applied pressure still varies as already described above.